Hi,
"Polygonize" should work well to vectorize the raster classes. If you
have problems with the file name, try simplifying the file name to the
bare minimun like c:\temp\toto.shp if you're on Windows. Make sure you
have no spaces or accents in the path (this includes the user path of
your operation system). Notice that there are two polygonize
algorithm. One is from QGIS and one is from GDAL. Try both. They are
probably both based on GDAL but one (probably the QGIS one) may have an
easier time with accents, spaces or special characters like '\n'.
Good luck
Nicolas
On 2022-03-29 7:51 p.m., Shinoto, PD Dr. Maria via Qgis-user wrote:
Hi Kirk,
that was helpful, thank you.
I am not yet where I need to be, but so far I could create two classes with the
formula found in the docs
(https://docs.qgis.org/3.10/en/docs/user_manual/working_with_raster/raster_analysis.html)
along this line:
`("slope@1" < 50) * 1 + ("slope@1" >= 50) * 2`
At this moment, my biggest problem is creating the vector file, the window
claims that the file name is too long. This cannot be the case, and the
directory itself should be OK. So now I am trying to get this done, and then I
will test three classes, which I did not get working up to now either.
If there are easy answers to these two questions, I would be pleased,
otherwise, I will try tomorrow.
Thanks a lot,
Maria
Am 30.03.2022 um 07:14 schrieb kirk <[email protected]>:
Hi Maria.
The symbology does not reclassify the underlying raster, it just changes the
way it is displayed. Use the raster calculator to generate a new raster with
the Classes you require. The native qgis calculator works well. You can find it
in the upper word menu under raster. Once you have your raster reclassified,
you can then convert it to a vector format
Kirk Schmidt
Sent from my Galaxy
-------- Original message --------
From: "Shinoto, PD Dr. Maria via Qgis-user" <[email protected]>
Date: 2022-03-29 6:32 p.m. (GMT-04:00)
To: qgis forum <[email protected]>
Subject: [Qgis-user] creating vector layer from slope map with few classes
Hi,
I have created a slope map from a DTM.
I have limited the symbology to three meaningful classes and wish to create a vector layer with
polygons of three classes from that. The conditions are One-Channel-Pseudocolor, Channel1
(Gray), interpolation discrete, modus "fortlaufend" -- not identical interval or
quantile, 3 classes with values <=20, 20 - 40, > 40.
The classes show up in the layer design panel symbology tab, but the layer
browser still (thankfully!) shows the greyscale ramp.
I wish to create a vector layer with polygons from the 3 classes.
All solutions I have looked up work under slightly different condition. After all I do
not know how to get the data of the DTM into three classes like
"Flat-Gentle-Steep"; I think the vectorization should work easily then.
Can anybody hint me to a solution?
Thanks and best wishes,
Maria
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--
Nicolas Cadieux
https://gitlab.com/njacadieux
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